A model system for studying chemical carcinogenesis in colon has been developed. Human colon can generally be maintained 14 days and rat colon at least 63 days as explant culture. Cultured human and rat colon have the ability to enzymatically convert various classes of chemical carcinogens, such as polycyclic aromatic hydrocarbons, N-nitrosamines, mycotoxins and hydrazines, into metabolites which react with cellular macromolecules, such as DNA and protein. A wide variation among people in the binding of both benzo(a)pyrene (BP) and 1,2-dimethylhydrazine (DMH) was seen. The data showed a skewed distribution which strongly suggested a distribution more complex than uni-modality. The carcinogen-DNA adducts for aflatoxin B1 (AFB), BP, N-nitrosodimethylamine and DMH have been identified and the persistence of the AFB-DNA modification have been studied in human colon. The effects of various suspected inhibitors and enhancers of colon carcinogenesis have been investigated on the metabolism of BP and DMH.